Thirteen litters of Osborne-mendel 19-21 day old rats were distributed so that half of each litter would be in one group (Donors) and the other half in another group (Recipients). The recipient group was distributed one/cage for five groups of 12 rats each. Each of the 5 recipient groups, was placed on diets containing 0, 0.1, 1.0, 5.0 or 56% sucrose. All donors were placed on a diet containing 56 percent sucrose and inoculated intraorally with 0.2 ml suspension of Streptococcus mutants 6715-15; one ml of the suspension was placed in the drinking water of the donors. On day one donors were placed with recipients. The mouths of all rats were swabbed daily, the swabs placed in PBS;, agitated and an aliquot was plated onto mitis salivarious agar. After 56 days blood and saliva were collected from the rats at the time of sacrifice. Data are presently being assimilated for 1) dental caries development, 2) natural transmission of S. mutans from donor rats to recipients, on 5 different dietary concentrations of sucrose, 3) ability of sucrose to support initial S. mutans inoculation, and 4) ability of natural infection to induce a secretory response.